There are numerous applications, particularly in the automotive and vehicular field, for a DC to DC converter which operates to provide a highly stabilized output voltage despite substantial variations in the supply voltage furnished by, for example, a 12 volt automotive battery.
One such application is involved in the generation of an AC excitation signal for a ultrasonic fuel injector; i.e., the ability to generate an excitation signal of controlled frequency and amplitude is at least in part dependent upon the stability of the DC voltage which is available to the excitation signal oscillator-generator.
In the fuel injection system application as well as in other applications, it is also advantageous to provide a reliable start up function for the converter oscillator and to minimize the number of required components for production economy.
An oscillator circuit with reliable start up characteristics is shown in FIG. 2.43 of "Design of Solid State Power Supplies", second edition by E. R. Hnatek, Van Nostrand Reinhold Company, page 78. In that circuit the primary winding of an output transformer in the oscillator output circuit is coupled to a tertiary winding in the oscillator input circuit to provide positive feedback. FIGS. 2-44 and 2-45 on page 80 of the same publication illustrate converter circuits having a feedback connection from the output circuit to the inputs of the oscillator for regulation purposes. However, these circuits are characterized by a large number of circuit components with a corresponding lack of production economy.